A court in Vietnam has jailed two men and two women for “organising others to flee abroad illegally” after Australia sent back a group of asylum seekers, their lawyer said.

The 46 asylum seekers, including the four defendants, were on board a small vessel intercepted off Australia’s west coast last year and were returned to Vietnam as a result of negotiations between the countries.

The four, who have been jailed for terms ranging from 24 to 30 months, were crossing the border illegally for the first time in July 2015 and their 42 Vietnamese companions were relatives and acquaintances, the lawyer Vo An Don told Reuters.

“It is our understanding these prosecutions do not relate to the illegal departure of those returned, but relate only to a small number of individuals who authorities allege are responsible for organisation of the venture,” the spokesman told Reuters on condition of anonymity, in line with departmental protocol.

New York-based Human Rights Watch, however, said the action violated the defendants’ fundamental right under international law to leave their own country.

“Vietnam has blatantly broken its promise to the Australian government not to prosecute boat returnees,” the group’s Australia director, Elaine Pearson, said.

Some of the returnees said that on their arrival in Vietnam, an official assured the group in front of the Australian consulate’s representatives that they would not be arrested or detained, according to HRW and Don.

Vietnam has been rebuked for its poor record on human rights, with dissidents, bloggers and religious figures having been jailed in recent years.